Jose wrote:

Every NDB approach in the country was authorized as a GPS overlay approach when the
overlay program came into being. Since then, these authorizations have been withdrawn
for any particular runway end when a stand-alone RNAV (GPS) approach was published for
that runway end.

You cannot use GPS for any final approach segment that is not retreivable from the
database, and for good reason: no approach RAIM and no approach sensitivity.

I can see that for GPS approaches, where you are relying on all the
gee-whiz stuff (sequencing and such), but when the GPS is substituting
for a dumb radio needle, the approach segment doesn't have to be
anywhere to give good course guidance (which is all the NDB does anyway,
and it can be argued how good it is).

I still don't see the safety issue which would prompt the FAA to balk at
this substitution.

I am not their advocate; just stating the facts as established by Flight Standards.

You might want to ask the man in charge, John McGraw, Director, Technical Programs Division,
Flight Standards Service, FAA, at their DC head-shed address.